Los Alamos researchers have demonstrated an almost four-fold boost of the carrier multiplication yield with nanoengineered quantum dots. Carrier multiplication is when a single photon can excite multiple electrons. Quantum dots are novel nanostructures that can become the basis of the next generation of solar cells, capable of squeezing additional electricity out of the extra energy of blue and ultraviolet photons.
“Typical solar cells absorb a wide portion of the solar spectrum, but because of the rapid cooling of energetic (or ‘hot’) charge carriers, the extra energy of blue and ultraviolet solar photons is wasted in producing heat,” said Victor Klimov, director of the Center for Advanced Solar Photophysics (CASP) at Los Alamos National Laboratory.
Getting two for the price of one
“In principle, this lost energy can be recovered by converting it into additional photocurrent via carrier multiplication. In that case, collision of a hot carrier with a valence-band electron excites it across the energy gap,” Klimov said. “In this way, absorption of a single photon from the high-energy end of the solar spectrum produces not just one but two electron-hole pairs, which in terms of power output means getting two for the price of one.”
Carrier multiplication is inefficient in the bulk solids used in ordinary solar cells but is appreciably enhanced in ultrasmall semiconductor particles – also called quantum dots -- as was first demonstrated by LANL researchers in 2004 (Schaller & Klimov, Phys. Rev. Lett. 92, 186601, 2004). In conventional quantum dots, however, carrier multiplication is not efficient enough to boost the power output of practical devices.
Nature Communications - Enhanced carrier multiplication in engineered quasi-type-II quantum dots
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“Typical solar cells absorb a wide portion of the solar spectrum, but because of the rapid cooling of energetic (or ‘hot’) charge carriers, the extra energy of blue and ultraviolet solar photons is wasted in producing heat,” said Victor Klimov, director of the Center for Advanced Solar Photophysics (CASP) at Los Alamos National Laboratory.
Getting two for the price of one
“In principle, this lost energy can be recovered by converting it into additional photocurrent via carrier multiplication. In that case, collision of a hot carrier with a valence-band electron excites it across the energy gap,” Klimov said. “In this way, absorption of a single photon from the high-energy end of the solar spectrum produces not just one but two electron-hole pairs, which in terms of power output means getting two for the price of one.”
Carrier multiplication is inefficient in the bulk solids used in ordinary solar cells but is appreciably enhanced in ultrasmall semiconductor particles – also called quantum dots -- as was first demonstrated by LANL researchers in 2004 (Schaller & Klimov, Phys. Rev. Lett. 92, 186601, 2004). In conventional quantum dots, however, carrier multiplication is not efficient enough to boost the power output of practical devices.
Nature Communications - Enhanced carrier multiplication in engineered quasi-type-II quantum dots
Read more »
